Refining of fatty oils, especially vegetable oils



Oct. 27, 1953 s. F. N. BIERKE 2,657,224

REFINING 0F FATTY OILS, ESPECIALLY VEGETABLE OILS Filed Sept. 9, 1950INVENTOR 5vome FHf/viof Ni/ason Bferke Patented Oct. 27, 1953 REFININGOF FATTY OILS, ESPECIALLY VEGETABLE OILS Svante F. N. Bierke, Lidingo,Sweden, assignor to Aktiebolaget Separator, Stockholm, Sweden,

a corporation of Sweden Application September 9, 1950, Serial No.183,970 In Sweden September 29, 1949 6 Claims.

The present invention relates to the refining of fatty oils, especiallyvegetable oils, in a continuous process.

The difierent working operations used when refining fatty oils,especially vegetable oils, are already known, and the literature in thisart shows that these operations can be arranged in varying sequence withvarying temperatures and reaction times for the diiferent operations.Depending upon which of the known methods is used, special advantagesare gained, such as a simple plant with subsequent low investment costs,low operating expenses, and the like. The common aim, however, is toobtain as a final product pure oil of good quality.

The process of the present invention differs from previous processes forrefining fatty oils, particularly in the temperature ranges, pressuresand reaction times used, and in the steps of the process where they areused.

The object of the invention is to provide a continuous process which, ina short time and without interruption, changes crude fatty oil into pureoil with the smallest possible loss of neutral oil; to provide such aprocess which requires a minimum of neutralizing agent for changing thecontent of free fatty acids in the oil into soapv stock; and to providesuch a process which may be practiced with simple, low-priced apparatus.

The invention is characterized chiefly as follows: Crude fatty oil andwater, possibly with some acid or carbohydrate added, are fedcontinuously into a mixer where they are thoroughly blended, and then,during a reaction time (differing in length with different oils)sufiicient for de-sliming the crude oil, the mixture is led through avessel so designed that slimy substances are prevented from settling init, whereupon the mixture is fed through a centrifugal separator inwhich it is split into a water phase rich in slimy substances, which areled away, and

an oil phase of a slime-free or nearly free nature, which is de-aerated.During this first stage of the process, heat is applied so that thewateroil mixture when entering the separator has a temperature of atleast 70 C. After this centrifugal separation, the oil phase, with itstemperature principally maintained, and a solution of a substanceneutralizing the free fatty acid content of the oil phase, such ascaustic soda or other alkali or a product comparable with it in itsaction, are passed under pressure into a mixer in which, during thelapse of 2 to 5 seconds, they are rapidly and intimately mixed with eachother. The ,mixture is then introduced, still in a con- 2 tinuous flow,into a hermetic separator of centrifugal type, in which the mixture issplit into a soapstock phase and a refined oil phase, both of which areled away separately. A maximum lapse of time of approximately 40 secondsis allowed from the moment the oil is mixed with the neutralizing agentuntil the refined oil is led away from the separator.

The de-sliming step, the first step in the refining process, is not initself novel. It is old, in de-sliming and de-gumming, to mix oil withwater in a cold state or at max. 30 C. and, after mixing, pass themixture through a heating apparatus which raises the temperature to amaximum of C., and then to separate the mixture in a centrifugalseparator and thus obtain oil which is mainly slime-free. It is alsoknown in the art that the refining of oil thus obtained can be continuedby mixing cold oil with a solution of a neutralizing agent for the freefatty acid of the oil, subsequently heating the mixture to C. duringgentle or diminishing stirring, and finally separating it in acentrifugal separator with two outlets, one for the soapstock andone forrefined oil.

However, the water requires a certain reaction time to act upon theslimy substances, and during this time a considerable amount of slimysubstances will normally precipitate. In order to feed to thecentrifugal separator a homogeneous mixture of oil and slime substancesand to help bring about a continuous operation, I avoid precipitation ofslime substances during a period suitable for the reaction, by conveyingthe wateroil mixture through a vessel specially installed for thispurpose and in which an even flow is maintained, for example, in avertical direction. The centrifugal separator will then operate smoothlywith a constant or nearly constant level between the two liquidcomponents which are separated in the bowl. This condition for thede-sliming constitutes an essential part of the present invention.

After the de-sliming operation, the method of mixing cold oil with aneutralizing medium for the free fatty acid of the oil, heating themixture during mild turbulence, and separating it in a centrifuge, hasproved less advantageous. The cooling of the oil before mixture and thesubsequent heating before separation means loss of time and heat. It hasbeen found of more advantage to de-aerate the oil, while maintaining thehigh temperature of the oil or even raising it further, and then to mixit rapidly and intimately with the neutralizing medium in a closed tank,for 2 to seconds under a pressure of preferably 4-5 l g./cm. Whilemaintaining the pressure, the mixture is led through a hermeticcentrifugal separator in which the mixture is split into a soapstockphase and a phase of refined oil, both of which are dischargedseparately, a maximum period of approximately 40 seconds being allowedto elapse from the moment the oil is mixed with the neutralizing mediumuntil the purified oil is discharged from the separator.

By this method, there is a saving of time and also of part of the heatwhich, in the prior processes, are required for the cooling and repeatedheating of the oil. Also, the apparatus will be simple to use and theinitial cost low. Another advantage of this part of the new process isthat the mixing of the still hot oil (the temperature of which isslightly below the initial temperature of preferably HP-80 C.) rapidlyand intimately with the neutralizing agent in a period of 2 to 5seconds, and the subsequent centrifugal separation in a hermeticseparator, during a maximum period of 40 seconds, results in theneutralizing medium reacting rapidly with the free fatty acids of thehot oil and neutralizing them. By effecting the separation in a hermeticseparator immediately after the reaction, the soapstock is separatedfrom the neutral oil as rapidly as it was formed, so that neither thesoapstocli nor the neutralizing agent will have time to aifect theneutral oil, at least in any degree worth mentioning, and saponify it.The slime and color substances which may remain in the oil afterde-sliming are also attacked by the neutralizing agent and aredischarged with the soapstock. The mixture, when introduced into ahermetic separator, is not subjected to a splitting action by theseparator, and therefore the formation of inseparable emulsions isprevented. The high pressure and temperature enable the soapstock to bedischarged from the separator as a soft sausage-like p'ulp withoutnecessitating special means of dilution. Although the neutralizingmedium is used in excess, 1. e. more of it than should be theoreticallynecessary, its total requirements are, however, small due to the crudeoil having first been de-slimed with water, a stage known by itself butused to particular advantage in the present process.

Special importance is attached to the rapid mixingof hot, de-slim'edoilWith the neutralizing medium, followed by arapid separation in ahermetic separator. The same good result in the quality and quantity ofthe oil is not obtained by mixingat lower temperatures and in the usualmanner for a period up to minutes duration with subsequent heating andseparation in an ordinary separator, or by a slow mixing operation atsuccessively rising temperature, until the stated temperature range isreached, followed by separation in an ordinary separator.

The importance of the rapid and'intimate'mixing of de-slimed oil withthe solution of neutralizing agent followed by a separation in ahermetic separator during a maximum period of 40 seconds, can beexplained theoretically in the following way:

Each finely divided drop of lye in the oil forms a globule in intimatecontact with the free fatty acids of the oil and with the neutral oil.In the first place, the lye in the surface film of the globule reactswith the free fatty acids and forms a soapstock envelope around theglobule, while the core'of the'latterconsists of pure lye. In

other words, the free fatty acids diffuse through the envelope of theglobule toward its center and are changed into soapstock. Due to thefact that both the soapstock and the lye are alkaline, they are capableof affecting the neutral oil and saponifying it. Of these two, however,the lye has the stronger saponifying action. If there is a long periodof reaction between the lye globules, on the one hand, and the freefatty acids and the neutral oil, on the other hand, the lye content ofthe globule is almost entirely neutralized and a saponification ofneutral oil takes place with the soapstocl; and the lye, if the latteris present in excess. If, after the dispersion of the lye drops in theoil, the mixture is subjected to vigorous stirring or a turbulencerendering it possible for a globule surrounded by soapstock to burstinto smaller-sized globules, this means that lye comes in contact withthe oil already nearly free of free fatty acid, and saponifies it. Eachbursting of the lye globules, once they are dispersed in the oil, istherefore detrimental, as is each prolongation of the reaction timebeyond a fixed length of time. Accordingly, it is essential that the lyeis dispersed in the oil, from the start, as rapidly and in as smallglobules as possible so that the reaction may set in immediately andsimultaneously in the entire cross section of the oil flow and continueduring the fixed length of time without the risk of the globulesbursting. The reaction is then rapidly interrupted by separation, andpart of the reaction may take place in the separator itself, which is ofthe hermetic type so that it will not cause the globules to burst.

A process according to the invention, for continuously refiningvegetable oil, is described in detail in the following, reference beingmade to the attached drawing in which the single illustration is adiagrammatic view of an apparatus for use in practicing the process.

Referring to the drawing, the oil to be refined is led by pump E throughpipe 2 to and through heater 3, in which the oil is heated to atemperature of -80 C. In counter-current to the oil, a heating mediumflows into the heater via pipe i and out through pipe 5. From the heater3, the hot oil fiows through a hand-regulated valve ii into a mixer '7.Water at the prevailing temperature is led into mixer 7 through pipe 8,which is fitted with a hand-regulated valve =9. The quantity of wateradded to the oil in mixer l amounts to 2 to 5% by volume of the oil andis preferably in excess of the quantity required theoretically forde-sliining the oil. Due to the water quantity being so "small, itsaddition means but a small reduction in the temperature of the mixturein relation to the temperature of the oil before mixing. The mixing iseffected quickly and efficiently in'the mixer "i, which conveys themixture to the top part of a vessel it. The latter comprises a closedvertical tube of a diameter and height calculated so that the mixturewill flow continuously from the top part to the 'bottompart'of thetubeduring the required reaction time between the water and the slime'matter :of the oil and at a speedat least egual to the settling speedof the slime substances (information or already formed) 'in .the oil.The reaction time varies for different oils, and the time of sojourn invessel H3 is as a rule about 30 minutes, "not more. From vessel '5 ii,the mixture is'led through ashort'pipe "II to separator 12, whichis'o'fthe centrifugal type. "In the latter, the mixture is separatedinto a water-phase of -s1imysubs'tances,

discharged through pipe I3, and a substantially slime-free oil phase,which flows out through pipes M and i5 to a heater IS. The oil passesthrough heater I6 in counter-current relation to a heating medium fed inthrough pipe I! and discharged through pipe is. While the heater i6 isnot necessary, in certain cases it is advantageous and brings the oil toa temperature of between 70-80 C. and substantially compensates for thefall in temperature in the previous apparatus. From heater I6, the oilflows to a de-aeration unit l9, where it is freed from possible airbubbles and other gases. The de-aerator l9 may be arranged in advance ofthe heater I6, if any. In certain cases, the unit Hi can be dispensedwith, if de-aeration is eifected in some other way at this point in theprocess. The oil is then conveyed by a pump 20, under a pressure of 4.-5kg./cm. into a mixer 2| fitted with a pipe 22 through which, at the samepressure, a pump 23 feeds to the mixer 2| a solution of a neutralizinmedium for the free fatty acids of the oil. The neutralizing agent maybe caustic soda or some other alkali or comparable product of thedesired neutralizing quality. The neutralizing agent is added in aquantity fixed in relation to the quantity of oil flowing per unit oftime and its free fatty acid content, but the quantity of neutralizingagent is in excess of that required theoretically. In the mixer 2|, theoil and the neutralizing agent are mixed rapidly and thoroughly for 2 to3 seconds while the temperature is maintained. There may, however, be aslight reduction of temperature caused by the neutralizing agent, whichis generally added at normal temperature. The mixture is then passedthrough a short pipe 24 into a hermetic separator 25 of the centrifugaltype, where it is separated into a soapstock phase within a period notexceeding 30 seconds, and a refined oil phase. The soapstock isdischarged through p'pe 26 and the oil through pipe 21.

The purified oil produced according to the invention has proved to befully comparable to the oils produced from the same initial materialwith the best current methods, but it is produced more quickly andsimply with lower installation and operating costs.

As with other methods used for refining oils of the kind underconsideration, the oil obtained by the present method can be furtherrefined by subsequent treatments.

I claim:

1. A method of refining fatty oils in a continuous flow, which comprisesfeeding a stream of the crude oil and a stream of Water to a mixing zoneand there effecting an intimate mixture of the oil and water, feedingthe mixture from said zone through a reaction zone for a periodsuflicient to de-slime the crude oil and while maintaining the mixturecontinuously in motion to prevent settling of slimy substances in saidmixture, passing the mixture from the reaction zone to a centrifugalseparator at a temperature of at least C. and there separating it into awater-phase rich in slimy substances and a substantially slime-freeoil-phase, separately discharging said phaSes from the separator,deaerating the oil-phase, feeding to a second mixing zone, underpressure, a stream of the oilphase at substantially said temperature anda stream of a neutralizing agent for the free fatty acids in the oil,quickly and intimately mixing said agent and oil phase in the secondmixing zone under a superatmospherie pressure for a period not exceeding2 to 5 seconds, passing the mixture from said last zone through a closedpath into a hermetic centrifugal separator and there separating it intoa soapstock-phase and a refined oil phase, and separately dischargingsaid last phases from the hermetic separator, the maximum periodelapsing from the moment the oil is mixed with said agent until therefined oil phase is discharged from the hermetic separator beingapproximately 40 seconds.

2. A method according to claim 1, in which the water is added to the oilin the first mixing zone in an amount in excess of the amounttheoretically required for de-sliming the oil.

3. A method according to claim 1, in which the crude oil is heated to7080 C. before it is mixed with the water in said first zone.

4. A method according to claim 1, in which the mixture of crude oil andwater is led through said reaction zone in a generally verticaldirection at a speed at least equal to the settling speed of the slimymatter in the oil.

5. A method according to claim 1, in which the de-slimed oil-phase fromthe first separator is heated to at least 70 C. before it is mixed withsaid neutralizing agent.

6. A method according to claim 1, in which the de-slimed oil and saidagent are mixed together in the second mixing zone under a pressure of 4to 5 kg./cm. the de-slimed oil and agent being introduced separatelyunder pressure into the second mixing zone.

SVANTE F. N. BIERKE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,157,069 Clayton May 2, 1939 2,182,755 Clayton Dec. 5, 19392,219,968 Thurman Oct. 29, 1940 OTHER REFERENCES M. K. Schwitzer, Ind.Chemist. 25,352-53 (1949).

Bailey, Industrial Oil and Fat Products (2nd Edition) 1951, pages638-39.

1. A METHOD OF REFINING FATTY OILS IN A CONTINUOUS FLOW, WHICH COMPRISESFEEDING A STREAM OF THE CRUDE OIL AND A STREAM OF WATER TO A MIXING ZONEAND THERE EFFECTING AN INTIMATE MIXTURE OF THE OIL AND WATER, FEEDINGTHE MIXTURE FROM SAID ZONE THROUGH A REACTION ZONE FOR A PERIODSUFFICIENT TO DE-SLIME THE CRUDE OIL AND WHILE MAINTAINING THE MIXTURECONTINUOUSLY IN MOTION TO PREVENT SETTLING OF SLIMY SUBSTANCES IN SAIDMIXTURE, PASSING THE MIXTURE FROM THE REACTION ZONE TO A CENTRIFUGALSEPARATOR AT A TEMPERATURE OF AT LEAST 70* C. AND THERE SEPARATING ITINTO A WATER-PHASE RICH IN SLIMY SUBSTANCES AND A SUBSTANTIALLYSLIME-FREE OIL-PHASE, SEPARATELY DISCHARGING SAID PHASES FROM THESEPARATOR, DEAERATING THE OIL-PHASE, FEEDING TO A SECOND MIXING ZONE,UNDER PRESSURE, A STREAM OF THE OILPHASE AT SUBSTANTIALLY SAIDTEMPERATURE AND A STREAM OF A NEUTRALIZING AGENT FOR THE FREE FATTYACIDS IN THE OIL, QUICKLY AND INTIMATELY MIXING SAID AGENT AND OIL PHASEIN THE SECOND MIXING ZONE UNDER A SUPERATMOSPHERIC PRESSURE FOR A PERIODNOT EXCEEDING 2 TO 5 SECONDS, PASSING THE MIXTURE FROM SAID LAST ZONETHROUGH A CLOSED PATH INTO A HERMETIC CENTRIFUGAL SEPARATOR AND THEREINTO A HERMETIC CENTRIFUGAL SEPARATOR AND THERE FINED OIL PHASE, ANDSEPARATELY DISCHARGING SAID LAST PHASES FROM THE HERMETIC SEPARATOR, THEMAXIMUM PERIOD ELAPSING FROM THE MOMENT THE OIL IS MIXED WITH SAID AGENTUNTIL THE REFINED OIL PHASE IS DISCHARGED FROM THE HERMETIC SEPARATORBEING APPROXIMATELY 40 SECONDS.